Show Caption ( + ) A memorial marking the anniversary of the Mt St Helens volcanic eruption appears in this picture, May, 29, 2000, on the site of Mt St Helens, twenty years on after the great eruption of May 18th 1980. (Photo by Dan Callister/Online USA) Hide Caption ( - )

Show Caption ( + ) MOUNT ST. HELENS, WA - NOVEMBER 22: In this handout frame grab, Mount St Helens lets off a plume of smoke as seen from the Johnston Ridge Observatory on November 22, 2005 in Mount St. Helens, Washington. The volcano came back to life in 2004 after lying dormant for many years. The plume of smoke was believed to have caused by a rock slide. (Photo by Johnston Ridge Observatory via Getty Images) Hide Caption ( - )

Show Caption ( + ) VANCOUVER, WA - MARCH 8: Mount St. Helens in Washington state is seen in this handout photo from the U.S. Geological Survey from the Cascade Volcano Observatory Office roof March 8, 2005 in Vancouver, Washington. The mountain released a towering column of steam and ash thousands of feet into the air as seismic activity signaled the reawakening of the 9,677-foot mountain. The volcano erupted on May 18, 1980, killing 57 people. (Photo by Matt Logan/U.S. Geological Survey via Getty Images) Hide Caption ( - )

Show Caption ( + ) MOUNT ST. HELENS, WA - OCTOBER 20: Lorraine Kells (L) and Susan Tyler (R), of Tacoma, Washington, view the crater on the north side of Mount St. Helens as a steam cloud vents from behind the old dome of the volcano October 20, 2004 at Mount St. Helens, Washington. Volcano activity became visible after several days of low clouds, rain and high winds. (Photo by Greg Wahl-Stephens/Getty Images) Hide Caption ( - )

Show Caption ( + ) MT. SAINT HELENS - OCTOBER 12: This handout photo taken October 12, 2004 by the U.S. Geological Survey shows Mount St. Helens' crater dome and uplift with new growth, as seen from the west. Scientists are keeping watch for an eruption as the volcano continually releases steam. (Photo by Jon Major/USGS via Getty Images) Hide Caption ( - )

Show Caption ( + ) VANCOUVER, WA - DECEMBER 19: A plume of condensation rises off Mount St. Helens, as viewed from the roof of the Cascades Volcano Observatory December 19, 2006 in Vancouver, Washington. The plume results from condensation of warm moist air rising off the growing lava dome. (Photo by Steve Schillling./The U.S. Geological Survey via Getty Images) Hide Caption ( - )